Fixing RSpec deprecation warning 'mock is deprecated. Use double instead.'
Add ability to hide trace flags/globally enable tracing

Adding ability to hide --trace, -t from the menu and globally enable
tracing via
https://github.com/visionmedia/commander/issues/16#issuecomment-329635

Don't show --trace text in error messages when it's disabled.
Rename commands to `always_trace!`/`never_trace!`

Improve spec to test behavior of commands
Merge pull request #67 from ggilder/jamesrwhite/add-tracing-switches

Add tracing switches